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| | | Junior Member
 
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Last Login: Thursday, November 22, 2007 8:12 PM
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| | Is the Y- Block lifter really a "mushroom" tappet. A mushroom tappet is a full diameter lifter with a larger diameter face to allow more radical cam timing. On the Y- Block you have most of the lifter the same dia as the pushrods, with only the face being full diameter. What is the face diameter of a Y- Block lifter? Bet its about the same as a SBF. There is no advantage there IMO. I don't think PHR thought this through correctly. I think they were just making life easier for themselves by eliminating one more possible reason the Chevy guys could complain about after they get their butts handed to them again. |
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| By definition, the Y-Block utilizes a mushroom lifter. A mushroom lifter is simply defined as a flat tappet lifter in which the wear face or lifter pad is a different diameter than the lifter body itself. In the performance world, mushroom lifters are synonymous with being able to run more aggressive camshaft profiles and hence the belief that a mushroom lifter is a performance lifter by design. Many diesel engines still utilize mushroom tappets but for no particular performance advantage. The wear pad on the Y-Block lifter is is actually larger than most of the other lifters out there in that it measures out at 1.00” so there could potentially be a performance advantage if the camshaft lobes were ground to take particular advantage of this. But after having a healthy discussion with the EMC representative on the phone, be assured that the Y was not disallowed because of any perceived performance advantage. The Y-Block engine itself was not disallowed, just the mushroom tappet lifters and this was made clear from the beginning in the rules.
  Lorena, Texas (South of Waco)
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| | Ted, A possible solution to the basecircle/lifter issue could be to overbore the camshaft tunnel and fit offset sleeves or bushes to raise the camshaft higher in the block, closer to the lifters. Not an easy fix, but it works in other engines when done. Inherent problem is the timing chain. Cheers Trevor |
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| Trevor. You’re right about the timing chain. Any serious thoughts about raising the camshaft in the Y forces the chain issue to be considered before all else. Other than this, raising the camshaft in the block sounds relatively simple but ultimately ends up creating some issues in regards to the lifter angles if these are not compensated for. Simply raising the camshaft and not relocating the lifter bores increases the lobe centerline for a given camshaft. On the Y, there is only 0.080” to 0.130” of lifter clearance to install the camshaft with the lifters placed at the top of their bores. Core shift during casting typically has each bank of lifters sitting with different clearances to the camshaft so this has to also be taken into account. Machining the bottom of the lifter bores so the lifter can be raised only compounds the problem in that the lifter bore itself now becomes even shorter. Relocating the lifter bores so that the camshafts intended lobe centerline angle remains the same when raising the camshaft gives a net gain of zero. With the stock camshaft journal sizes, the camshaft base circle still ends up being the limiting factor in getting more cam lobe lift while using the stock lifters. Going to a non mushroom lifter design gets around most of this.
Lorena, Texas (South of Waco)
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